Because the danger is different. The danger of AGI is that if it happens, it's an exponential process in which a machine basically instantly becomes so much smarter than the smartest human beings that it could circumvent any safeguards we humans could possibly think of, let alone put into practice.

What form might that take? No one can know because it is literally beyond our ability to comprehend. Perhaps a device that was smart enough could influence human minds at a distance using the em radiation from it's own circuits. Maybe it could take over a car, a Roomba, or an attack drone. Maybe it could manifest reality through sheer willpower.

Thats the problem with superintelligence; it's unpredictable. Add to that that perhaps humanity doesn't, um, have an unassailable claim to universal moral high ground, and there's a case to be made that a superintelligent AGI might decide that we humans gotta go.